This invention relates generally to electrical weighing systems and pertains particularly to strain gage weighing devices for fork lift trucks.
One type of prior art fork lift weighing scale utilizes the deflection of the horizontal position of fork tines as a measure of the weight of items placed on the fork. Such an apparatus is shown by Pien in the U.S. Pat. No. 3,059,710. Pien discloses a double cantilever type of reversing plural member tine having electrical resistance strain gages attached. A problem with this type of structure is that thickness of the fork tines must be large in order to incorporate the strain gages and in order to accommodate the double cantilever type of reversing plural member. Load cells attached to a bar mounted on the tines of a fork lift truck are disclosed by Cellitti et al in U.S. Pat No. 2,935,213.
Another prior art fork lift weighing system incorporates an auxiliary crossbar attached to the fork lift crossbars through a system of flexures. Movement of the auxiliary crossbar with respect to the fork is sensed by vertically disposed load cells. The flexures form a parallelogram type of structure and cause the load cells to be subjected only to vertical loads. Providing an auxiliary crossbar, load cells, and flexures is economically expensive and may obstruct the vision of a person operating a fork lift truck. Additionally, mounting an auxiliary crossbar and flexures on existing fork lift trucks requires that the forks be spaced horizontally away from the fork lift truck to allow the auxiliary crossbar, flexures and load cells to be mounted between the fork lift truck and the forks. Spacing the forks away from the fork lift truck may substantially decrease the load carrying capacity of the fork lift truck and produce an unsafe condition since such a weighing system reduces the weight of load which will tip the fork lift truck. By placing the forks further from the fork lift truck, the overturning moment is achieved with less weight on the forks since the lever arm is increased. The overturning moment can be defined as the moment required to tip the fork lift truck. A mechanical scale mechanism is shown by Anderson et al in U.S. Pat. No. 2,940,746. Anderson et al discloses a scale mechanism which may be incorporated as a part of the fork or platform carriage of a lift truck. Anderson et al describes a cantilever type weighing platform suspended from a weight indicating mechanism which, in turn, is suspended from structures attached to a fork lift truck.